The present invention is directed to a brake device and, more particularly, to a brake device that is supported by fixing pins which extend from seats provided to the frame of the bicycle, and that is driven by a brake cable so as to press brake shoes against the rim of the wheel.
A cantilever type of brake device is generally mounted on bicycles designed for off road use, such as those called mountain bikes (MTB) and all-terrain bikes (ATB), in order to provide a powerful braking force. A cantilever type of brake device is equipped with brake arms, which are rotatably supported in cantilever fashion on the front or rear fork provided to the front and rear of the bicycle frame, and with brake shoes, which are fixed in the middle of the brake arms. One end of the brake arms is rotatably supported on the frame, and the other end is linked to a brake cable. The brake shoes are arranged opposite one another on either side of the bicycle wheel rim in the middle of the brake arms.
With this cantilever type of bicycle brake device, the brake arms rotate in the closing direction when the brake cable is pulled by the brake lever, and as a result the brake shoes are pressed against the rim and apply a braking force. With such a cantilevered brake device, there is no need to vary the shape of the device with the size of the bicycle, as is the case with a caliper brake device, and this is advantageous in that a more equal braking force is applied on the left and right, rather than the brake working on just one side.
However, when the brake shoes rotate downward from the horizontal plane as a result of the rotation of the brake arms with a cantilevered brake device, the pressing force is diminished if the brake shoes come into contact with the side of the rim without matching up with the slope thereof. Consequently, the relative attachment positions of the rim side surface and the brake device must be adjusted precisely, but this adjustment work is difficult.
A four-link type of brake device is one form of prior art that solves this problem. This four-link type of brake device comprises brake arms which are slidably supported on fixing pins that extend from seats, and the upper ends of which are positioned to the outside of the fixing pins; output links that are rotatably supported in the middle of the brake arms and extend to the outside; follower links that are rotatably linked to the output links and extend downward; and stationary links that are rotatably linked to the follower links and extend to the inside so that they are non-rotatably linked to the fixing pins. The brake shoes are attached to the middle of the output links. With this brake device, when the brake arms are rotated upward by the brake cable, the follower links rotate to the inside, and the output links move horizontally or upwardly. As a result, the brake shoes hit the rim side surface.
With the above-mentioned structure, the frictional force of the bolt threaded into the tip of the fixing pin is utilized to link the stationary link to the fixing pin so that the stationary link does not rotate relative to the fixing pin. Consequently, when a powerful braking force is applied to the brake shoes, the stationary links are sometimes rotated against this friction by reaction force, so the brake shoes escape from the sides of the rim and a sufficient braking force is not obtained. Also, a sufficient braking force sometimes cannot be obtained when the stationary links are caused to rotate by a loose bolt or by chatter.
Furthermore, since the output links to which the brake shoes are attached are linked in cantilever fashion to the brake arms, when a reaction force acts on the brake shoes during braking, the reaction force can cause the linked portion to chatter and twist. When such chatter or twisting occurs, it allows the force that would otherwise be obtained with a four-link system to escape, so a powerful braking force is not obtained.